README.md

sim/xsim/ — second-simulator gate (Vivado xsim)

make xsim runs the directed unit suite (tests/*.s) under Vivado xsim — the simulator the host SoC integrates with — instead of Verilator. It exists because two integrator-reported defects (the LMB back-to-back stale read and the continuous-assign forwarding-sensitivity gap) lived in the semantic delta between Verilator and xsim, and Verilator computed the correct answer regardless of stimulus, so no Verilator vector could catch them. See docs/verification.md §4.1.

Files

File	Role
run_xsim.ps1	runner (PowerShell, Windows-native): WSL builds hex → xvlog/xelab once → xsim replays each hex → score PASS/FAIL
../../tb/xsim/tb_xsim.sv	SV testbench driver: the analogue of tb/cpp/sim_main.cpp (clk/reset/irq/timeout/tohost-detect over tb_top)

Run

pwsh sim/xsim/run_xsim.ps1                 # all tests/*.s  (WSL assembles hex, then xsim)
pwsh sim/xsim/run_xsim.ps1 -NoBuild        # reuse existing sim/build/*.hex
pwsh sim/xsim/run_xsim.ps1 -Tests fwd_matrix,loadbase_fwd,bus_patterns
pwsh sim/xsim/run_xsim.ps1 -VivadoBin 'D:\Xilinx\2025.2.1\Vivado\bin'

Exit 0 = all PASS; nonzero = any FAIL/TIMEOUT. Generated artifacts go to work/ (git-ignored).

Requirements

• Vivado (xvlog/xelab/xsim) on Windows — auto-detected, or -VivadoBin/$XILINX_VIVADO.
• WSL distro with the riscv toolchain (default Ubuntu-24.04, -WslDistro to override) to assemble the tests; or pre-build hex in WSL (make -C sim test) and pass -NoBuild.

Implementation notes (xsim quirks the runner works around)

• The xsim.bat wrapper splits a name=value arg on = and chokes on a drive-letter colon, so plusargs are passed through a per-run .bat with the value quoted (--testplusarg "hex=foo.hex") and the hex is referenced by a bare relative name from the work/ cwd.
• --runall must be a CLI flag (it has no effect from a -f command file).
• The runtime flags are double-dash (--runall, --testplusarg, --onfinish).